Pin grid arrays (PGAs) are commonly used in the microelectronics industry, for example, for connecting a chip module to a printed circuit board or printed wiring board, utilizing pins in an area under the module that plug into a corresponding socket on the printed circuit board. Alternatively, the module may utilize a socket in an area under the module which is adapted for receiving corresponding pins mounted on the printed circuit board. PGAs are commonly, although not always, referred to as zero insertion force (ZIF) connectors. The term “ZIF connector” generally refers to a socket arrangement wherein when the socket is open, a chip may be placed in the socket without any pressure at all, and when the socket is then closed, the contacts of the socket grip the pins of the chip. Micro-PGA sockets typically refer to a PGA socket configured having a pin spacing, also referred to as pin pitch or simply pitch, between adjacent pins that is about 1.27 millimeters (mm) or less.
Micro-PGAs are often preferred to other types of area array sockets, such as, for example, land grid arrays (LGAs), primarily because assembly and disassembly are much easier and do not require actuating hardware with posts that extend through the printed circuit board. PGA sockets are often soldered to the printed circuit board in a surface mounted fashion. The module typically has pins extending downward. In a ZIF arrangement, the module and socket on the PCB are typically brought together such that the pins are inserted all at once into corresponding contact holes in the PGA socket, and then the socket contacts are brought into electrical and physical contact with the pins using a mechanism that moves a top plane of the socket laterally, thereby engaging each pin to the respective electrical connection at that grid location.
Most high input/output (I/O) count chip modules (e.g., greater than about 100 pins) currently use a 1.00 mm pitch to interconnect to the printed circuit board, either by soldering, as ball grid arrays (BGAs), or by socketing with LGAs. PGAs, in contrast, are most commonly used on smaller I/O modules and often at a 1.27 mm pitch. PGA suppliers are now attempting to fabricate PGA sockets that have a large I/O count at a 1.00 mm pitch, but are struggling to achieve a 50 mm×50 mm array size. Conventional interconnection methodologies appear to be approaching a natural limit based at least in part on characteristics of the injection molding process typically used to fabricate the plastic component parts. For example, injection molding parts with sufficient uniformity and flatness is difficult, in part because the large area of a 50 mm×50 mm array makes the transport of molten plastic from the injection ports to all mold areas difficult and in part from shrinkage and thermally induced stress across the array. This precludes making PGAs as a single molded piece for large substrates such as those currently serviced by LGAs with I/O pin counts greater than about 7000.
Accordingly, there exists a need for an improved PGA-type microelectronic interconnection capable of providing substantially large I/O pin counts (e.g., greater than about 7000) that does not suffer from one or more of the problems exhibited by conventional PGA-type area interconnections.